1. Field of the Invention
The present invention relates to a pinch valve assembly capable of closing a passageway through a soft tube by pressing a slider that can advance in and retreat from a housing against a portion of the soft tube and more particularly to an improvement to protect the operability of the tube.
2. Description of Related Art
In a pinch valve assembly of this type, a slider can be advanced and retreated by means of a solenoid to close a flexible tube. In a biased-opened pinch valve, the slider is moved to a position where it continually presses against a soft tube, by electrifying the solenoid and it is returned to an initial position, where it does not press against the soft tube, when the solenoid is not driven. On the contrary, in a biased-closed pinch valve, the slider is moved to a position, where it does not press against the soft tube, by electrifying the solenoid and it is subsequently returned to an initial position, where it constantly presses against the soft tube, during the time period when the solenoid is not electrified.
In the above described conventional pinch valve and particularly in a biased-closed pinch valve, the soft tube frequently assumes an inoperative condition when the slider is constantly pressed against it during a passive mode of operation so that the soft tube can become stuck or can be closed under the influence of plasticizers contained therein, when it has not been used and/or can be subjected to a plastic deformation due to the continuous pressing of the slider thereagainst and accordingly damaged. Such conditions can occur when the tube is not subject to pressure fluid conditions, such as during storage or prolonged inactive periods of time.
In order to avoid such a situation, the slider pressing against the soft tube has been attempted to be varied in shape and material. In addition, attempts have been further made to avoid such problems by removing the soft tube from the housing during such time periods, such as transportation and storage, and when it is not used, but a problem has occurred in that the operation for removing and reinstalling the soft tube is particularly troublesome to the technicians.